1. Field of the Invention
The present invention relates to aqueous emulsions of pressure-sensitive interpolymers containing 2-acrylamido-2-methylpropanesulfonic acid and to articles of manufacture comprising surfaces coated with such pressure-sensitive interpolymers.
2. Description of the Prior Art
Pressure-sensitive resins are used conventionally in the form of films to provide adhesive bonds between normally non-adhering surfaces. The films are conventionally prepared by casting them from organic solvent solutions of pressure-sensitive interpolymers and evaporating the solvent. The disadvantage of such organic solutions arises from the large quantities of organic solvent effluent which is discharged into the atmosphere. Manufacturers of pressure-sensitive articles are, therefore, switching increasingly from organic solutions to aqueous emulsions of the pressure-sensitive interpolymers to minimize atmospheric pollution.
Acrylic resins are among the interpolymers used as pressure-sensitive resins. When they are prepared in aqueous emulsion and coated on a substrate to yield a pressure-sensitive film, they exhibit poor age resistance manifested in a substantial loss of peel strength. There is, therefore, a need in the art for pressure-sensitive acrylic resin emulsions which yield pressure-sensitive films with adequate age resistance.